fitting plasterboard with foam: never again!

[george - dicegeorge]

Arrow in Leominster now stock pinkgrip in cans with plastic tubes, so you dont need to buy an applicator gun.

[g]

[Bert Coules]

Good advice, thanks. I'm pretty sure that this is the root of my problems. I've only ever used the spray cans.

Bert

[Tim Watts]

On Wednesday 22 May 2013 11:04 Bert Coules wrote in uk.d-i-y:

I tried a spray can once - utterly crap IME compared to even a cheap gun.

[Grimly Curmudgeon]

It's the way I did it - worked, no problems. I ran narrower beads of normal (not low-expansion) foam around the periphery, criss cross, and filled in the spaces with blobs and whorls. Propped it into place, kept pressure on it for two hours and it stuck like shit to a blanket.

[Fred]

Hi. Thanks for all the replies. Sorry I haven't replied to any of them; I've been busy plastering and haven't been on Usenet for a few days. I've only come on today to post about my broken multi tool. When I get the room finished in a day or two, I'll post an update.

[ben.handley1988]

Hi Guys,

I have a quick question. I am in the process of converting /restoring an old victorian house. Taken a lot of walls back to brick and run in new plumbing and electrics. My question is....... how would you dryline (using foam) around new electrical back boxes ? would the foam give you the depth?

Not sure if anyof you will get this message but any advice is appreciated.

cheers

Ben

[Jim K]

use drywall backboxes that fix onto the pb?

Jim K

[Dave Plowman (News)]

Do the dry lining first, and fit the boxes afterwards. Cables can be run in before the board, though.

[sm_jamieson]

old victorian house. Taken a lot of walls back to brick and run in new plum bing and electrics. My question is.......

ld the foam give you the depth?

The foam would give you up to about 25mm gap I would say. The trouble with fitting back boxes first is getting the holes cut in the correct place - ca n be done though. A trick on DIY SOS I saw once was to put the plasterboard against the wall with backboxes and "bang" it to create an impression of t he back box. I tried this and it sort of works. I also tried putting ink on the back box to mark the plasterboard, which sort of works too. But it never fits quite as well as you expected ! The difficulty with fitting the boxes after, especially if the wiring is in place, is getting the box into the hole whilst the wires are blocking the hole. The best thing I found is to cut into the plasterboard to give more p lay in the cables, then fill this with some plaster afterwards. I'm not sure how the pros would do this type of job. If the wall/PB gap is enough you can fit hollow wall boxes of course.

Note: if using foam, include some mechanical fixings near the top for safet y in case of fire, etc. You can get some special fixings for this purpose. I've not used them but I assume they are like hammer-in frame fixings but w ith a broad shallow head on top (I've just visualised Stewie from Family Gu y). Simon.

[Dave Plowman (News)]

It can - but it's twice as much work. You have to line up the boxes perfectly on the wall, then cut out the holes perfectly too. Not worth the hassle.

[SteveW]

As plasterboard is non-combustible, it doesn't matter if the boxes only reach the back of the plasterboard. I fixed my backboxes into the blockwork and made measurements to the centre of each box. Plasterboarded over the top and then cut out each one from its centre - taking care to ensure the cables were right at the back of the box and the cutting blade was too short to reach them.

It effectively makes your 25mm boxes 35mm ones, so more room to manouver and leave decent tails.

SteveW

[sm_jamieson]

an old victorian house. Taken a lot of walls back to brick and run in new p lumbing and electrics. My question is.......

would the foam give you the depth?

ith fitting back boxes first is getting the holes cut in the correct place

- can be done though. A trick on DIY SOS I saw once was to put the plasterb oard against the wall with backboxes and "bang" it to create an impression of the back box.

box to mark the plasterboard, which sort of works too. But it never fits q uite as well as you expected !

s in place, is getting the box into the hole whilst the wires are blocking the hole. The best thing I found is to cut into the plasterboard to give mo re play in the cables, then fill this with some plaster afterwards.

Aha - just remembered I did that too. Simon.

[Piers]

I batten my walls to attach the insulation+plasterboard to. I then wire up _and_ fix the back boxes. I then hold the plasterboard in position and tap (as was suggested) leaving an indentation. I then cut the right bit out with a plasterboard saw. It found it works pretty well, although you really need a helper - holding a bit of 8x4 with 70mm insulation+plasterboard in place while tapping is tricky!

[Piers]

Do you have a link to the sort of fixings you're talking about?

[Dave Plowman (News)]

Surely it's far more difficult fixing boxes to the wall good and square than cutting holes in plasterboard to do the same thing?

[spuorgelgoog]

I disagree, especially with dry-lining boxes which rely on the accessory screws to hold them in.

At least with proper boxes once you've drilled/plugged/foamed/plastered them in they're unlikely to move[1] and stay straight[2].

[1] Apart from the ones I put in, admittedly [2] Unlike the drylining boxes with always move off straight while I do them up.

Owain

[SteveW]

Not in relatively soft blockwork. I wasn't bothered about mess and just used old, sacrificial router bits in my router to rout out perfectly flat bottomed, square holes for boxes and nice, straight edged chases for the cables at the same time.

SteveW

[Dave Plowman (News)]

Ah. Might be with blockwork. Was more thinking of bricks. Ie, old house rather than new build.

[Dave Plowman (News)]

I never use dry lining boxes.

If you have a solid wall behind the plasterboard, simply do the cutout for a steel back box and fix it to the wall. You may have to either chase out the wall a bit, or add packing to get the box level with the board. Still easier than doing all that on the wall then trying to get the plasterboard to fit the boxes.

[Piers]

Ooops - I realise today that this (oldish) thread was using foam to fit plasterboard. In my jetlagged state I didn't bother to reread the OP and assumed it was fitting "foam-backed" i.e. insulated plasterboard. (More embarrassing cos I did read the thread when first posted.) Ignore me!